This invention relates to a method of, and an apparatus for, obtaining individual web sections from a web of sheet material, for example, to a method of, and apparatus for, forming bags from a length of a sealable sheet material.
In GB-A-1052701 there is described a method of making bags of a thermoplastic synthetic resin film comprising tube-making means including a pair of cooling means disposed between a guide roll and take-up rolls along the advancing direction of the film or films and in the vicinity of the edges at the two sides of the sheet or sheets to be sealed, the cooling means having a gap therein for cooling the films by the slidable movement of the films therethrough, heating means disposed in proximity of the film edges which protrude beyond the cooling means, and another cooling means disposed next following the heating means and on the same side as the heating means relatively of the film edges; a severing means for cutting the thermoplastic synthetic resin film tube whose edges have been completely sealed together by said tube making means, in predetermined lengths at right angles to the advancing direction of the film tube; and a bag bottom sealing means having heating means for fusing together the severed edge of the film tube. This bag bottom sealing means is provided at right angles to the tube-making and severing means; hence a conveying means consisting of an accelerating stacker and a direction-changing stacker is interposed between the tube-making and severing means and the bag bottom sealing means. In this arrangement the bag to be formed travels transversely to its former direction of motion and the bottom seal is formed in the new direction of the bag. This design is, by modern standards, incapable of achieving the high bag formation speeds desired today.
U.S. Pat. No. 4,005,970 teaches an apparatus for continuously producing seals in tube-shaped plastics film material comprising means for supplying the web of material, at least one heating beam travelling along with the web and subsequently returning, means for keeping the web mechanically tension-free at the location where it is warm, means for keeping the heated film layers one against the other up to a pressing station, said pressing station comprising two rollers at least one of which is provided with cooling means, and means for discharging the web. There is no description of what happens upon discharge of the web from the apparatus described, but since the web is to be formed into bags the web is presumably cut into bag lengths downstream from the apparatus described.
In U.S. Pat. No. 4,061,458 there is taught an apparatus for processing a web of material without a standstill. This has a pair of confronting transverse tools between which the web is guided. The tools are mounted on carriers guided in pairs on endless chains to follow a path composed of two parallel straight sections joined at the ends by semi-circular sections, the latter being relatively adjustable.
A bag-making machine is described in EP-B-0333726 in which the bags are defined by lines of perforation and weld lines. The cutting means used to form the perforations and the welding means are described as being separately connectible and disconnectible independently of other means.
U.S. Pat. No. 3,147,168 is concerned with manufacture of bags in the form of a series of connected bag sections open at their upper ends. It describes an apparatus in which registration of the seals between successive printed areas is maintained as the bags are formed. The bags are first sealed and then cut in turn from the web.
A similar principle is illustrated in U.S. Pat. No. 4,061,458.
GB-A-1147466 teaches a machine for making bags with an arcuate bottom using a conventional bag making machine which comprises in combination a mechanism for unwinding a film roll, a mechanism for transversely welding the unwound film at specified intervals in the longitudinal direction of the film, a mechanism for transversely cutting the welded film either in front of or behind the weld line thereby to form bags, and a mechanism for extracting the bags thus formed and collecting them in a specified place.
In modern day packaging there is a demand for machines that are capable of working at ever higher and higher speeds, while still producing packages with reliably formed seals and of neat appearance.
Roast and ground coffee is packaged in some countries in bags at atmospheric pressure so that the coffee more or less loosely fills the bag. However, in some countries the consumer is used to purchasing roast and ground coffee in vacuum packed packages. Such packages conventionally have a parallelepipedal shape, somewhat reminiscent of a brick. It is difficult to produce vacuum packages without unsightly wrinkles in the packaging material.
In order to facilitate the formation of a neat vacuum packed package of coffee, it is often packed in gusseted bags. These are typically formed from a tube of thermoplastic material which is itself made by sealing longitudinal edge portions of a web of thermoplastic sheet material one to another. The tube may then be provided with longitudinal creases so as to form a flattened tube at the lateral edges of which panel portions have been folded inwardly to form gussets. However, to form the bottom seal of a bag with gussets it is necessary to supply heat from a pair of opposed external heating bars through four layers of thermoplastic material, an operation that requires a significant time to perform, since the thermoplastic material is normally a relatively poor conductor of heat and it is at the inside surfaces that the thermoplastic material must be heated to welding temperature in order to form a reliable seal. Thus it may require the heating elements to be kept in contact with the outer faces of the flattened gusseted web for a period of from about 0.3 to about 0.75 seconds and under pressure in order to form a reliable seal, depending upon the thickness and thermal conductivity of the thermoplastic material.
An additional problem is that the web is usually preprinted with repeating patterns, each pattern providing advertising material and product information for each successive bag. Normally the web is printed with repeating registration marks for enabling the machine to be adjusted while it is running so that the bottom seals in the bags are in the correct relationship to the printed pattern and so that the bags are severed from the web with the printed information in the correct place thereon. By providing mechanisms for holding a portion of the web temporarily in a buffer along the path of the web and by arranging that at some point in the cycle of formation of each bag the sealing mechanism is out of contact with the web, then the correct print registration can be achieved by temporarily speeding up or slowing down the web as it passes through and between the various stages of the formation of a bag, so that the repeating printed pattern can be restored to the correct registration with the bottom seals. If the web is continuous, then in a high speed machine, the sealing section for forming the bottom seals of the bags may have to be relatively long, in order that each bag can spend sufficient time in contact with the heated elements and under pressure in order to achieve a reliable bottom seal. Once the bottom seal has been made, then the bags can be severed in turn from the web. However, if the speed of operation of the machine is sufficiently high that the time needed to form a reliable seal is greater than the interval between severing one bag and the next from the web, then in such an arrangement it is necessary to provide more than one set of sealing stations along the path of the bags in order to provide a sufficient sealing period for creating a reliable bottom seal and yet to permit print registration to be achieved. In this case a convenient place to achieve the necessary speed adjustment is in the middle of the bag bottom seal sealing section. However, if the heating elements part company from the outside of the web, the web will cool and further time has to be allowed for the interior of the web to achieve the correct welding temperature, when the web again contacts the downstream heating elements, thereby further lengthening the time required for forming the bottom seal of the bag. In addition it is difficult, even when print registration is satisfactory, to ensure that the second and any succeeding pair of sealing elements contacts exactly the same area of the web that was contacted by the previous pair of sealing elements. During adjustment of print registration the second and any succeeding pair of heated elements will not contact exactly the same area, since the web will have been moved, typically by about 0.25 mm, relative to the second and any succeeding heated elements by the print registration adjustment mechanism. Hence the security of any end seal formed during adjustment of print registration is far from satisfactory.
It would be desirable to provide a high speed method of, and apparatus for, obtaining individual sections from a web of sheet material upon which a predetermined process has been performed. It would further be desirable to provide a bag forming machine in which the sealing section used to form the bottom seals of the bags is relatively short and in which the heating elements are kept in contact with the web at all times as it passes through this sealing section. It would be further desirable to provide a high speed bag making machine in which registration of a print pattern with the bottom seals can readily be achieved without disrupting the sealing step used to form the bottom seals of the bags and hence endangering the security of such seals. In addition it would be especially desirable to provide a machine and method for making gusseted bags at high speed, while maintaining print registration in relation-to the bottom seals as they are formed.
The present invention accordingly seeks to provide a high speed method of, and apparatus for, obtaining individual sections from a web of sheet material upon which a predetermined process has been performed. It further seeks to provide a method of making bags at high speed, for example at a rate of from about 200 to about 300 bags per minute, in which the bottom seals of the bags can be reliably formed. It further seeks to provide such a high speed method of making gusseted bags with reliable bottom seals. Yet again it seeks to provide a method of making bags at high production speeds and with great reliability in which print registration can be readily achieved without prolonging the time required for forming the bottom seals of the bags. In addition it seeks to provide apparatus capable of carrying out such methods.
According to the present invention there is provided a method of obtaining individual web sections from a web of sheet material, each web section having a predetermined process performed upon it, comprising the steps of:
(i) feeding a web of sheet material along a feed path to a severing station, said web carrying a succession of repeating features;
(ii) severing the web at positions related to said features so that individual web sections are obtained, each carrying at least one predetermined feature;
(iii) feeding said individual web sections to a processing station; and
(iv) carrying out a predetermined process at said processing station in which a predetermined portion of each web section is maintained in registration with a processing element for a predetermined period thereby to effect said process on the web section.
In step (iv) of the method of the invention the predetermined period can be longer than the period between severing of that individual web section from the web and the severing of the next succeeding individual section from the web.
In such a method the repeating features can be features of shape, pattern or other markings. In the method of the invention the individual web sections are preferably fed longitudinally along the feed path to the processing station. Preferably the severing step is carried out so as to maintain the line of severing of each web section from the web in registration with a selected feature on the next web section to be severed from the web. The selected feature can be a registration mark. Preferably severing of the web into individual web sections is effected by means of a rotary knife mounted for rotation about an axis transverse to the direction of feed of the web cooperating with a counter blade, which may be fixed or may rotate, and maintenance of the predetermined portion in registration with the processing element is achieved by temporarily varying the feed speed of the web with respect to the speed of rotation of the rotary knife, when the desired registration is disturbed, thereby to effect a corresponding temporary variation in the length of the individual web sections until the desired registration is re-established. Preferably the rotary knife and the processing element are driven in synchronism.
The severed web sections are preferably fed to and through the processing station at the same speed as or at a speed greater than the speed of feeding the web to the severing station.
In carrying out the method of the invention the predetermined portion of each web section is desirably maintained in registration with the processing element for said predetermined period while passing along a predetermined portion of the feed path.
The web can be in the form of a tube having a longitudinal seal thereon. Moreover the tube can be formed with longitudinal gussets. It is further preferred for the web to be pre-creased longitudinally along lines corresponding to the lines of the gussets.
The web preferably comprises sealable sheet material having a sealable face, whereby when the web is severed into web sections corresponding to bag lengths the inner faces of the bag lengths comprise said sealable material, and said process comprises forming a bottom seal in an individual bag length by causing adherence of predetermined portions of said inner faces one to another. In this case the web may comprise a cold sealable or pressure sensitive sealable material which can be sealed by application of pressure alone at ambient temperature. However, the web may alternatively comprise a heat sealable material, in which case said processing step may comprise applying heat and pressure to a predetermined portion of the outside of a bag length. The individual bag lengths may be gussseted. If the bag lengths are adapted to be opened up and filled to form a substantially parallelepipedal package, then it is preferred if the web is pre-creased along transverse lines corresponding to at least one edge of the package selected from a top edge and a bottom edge thereof.
In a particularly preferred method according to the invention, the web is a web of sealable sheet material and is severed into bag lengths, and the processing step comprises formation of a bottom seal in each bag length; this method comprises feeding the web along a feed path from a supply thereof, forming the sheet material into a tube by sealing opposite longitudinal edge portions of the sheet material one to another, feeding the tube in flattened form further along the feed path to a severing station, severing the flattened tube in passage through the severing station into individual flattened bag lengths, feeding the individual flattened bag lengths longitudinally along the feed path to a sealing station, and applying pressure to opposite faces of an end portion of each flattened bag length as it passes through the sealing station for a predetermined period, which is longer than the period between severing of that bag length from the flattened tube and severing of the next bag length from the flattened tube, while continuing to feed the flattened bag length longitudinally along the feed path thereby to form a bottom seal for the bag. In such a method the web may comprise a heat sealable material, in which case the predetermined process will include also application of heat, simultaneously with pressure, to opposite faces of the end portion of the bag length as it passes through the sealing station. In such a method the sheet material is preferably fed from the supply along the feed path to the severing station at a first feed rate and the individual bag lengths travel from the severing station to and through the sealing station at a second feed rate that is greater than the first feed rate. The sheet material fed from the supply thereof can be pre-printed with a succession of repeating pattern lengths, each corresponding to a bag to be formed and each including print registration indicium means to facilitate correct registration of the respective pattern length on the bag during its formation.
The sheet material can be formed into a tube by sealing edge portions of the web one to another so as to form on the tube a longitudinal fin seal or a longitudinal lap seal. It is also envisaged that the tube may be provided with longitudinal creases before it is flattened whereby the bag is provided with gussets as the bottom seal of the bag is formed. The flattened tube may comprise first and second outer panels, a pair of first inner panels, and a pair of second inner-panels, the first outer panel being bounded by first longitudinal outer creases each of which separates it from a respective one of the.first inner panels and the second outer panel being bounded by second outer longitudinal creases each of which separates it from a respective one of the second inner panels, and each first inner panel being separated from a respective second inner panel by an inner longitudinal crease. In such cases it is also preferred that the first longitudinal creases are each substantially aligned laterally with a respective corresponding second longitudinal crease in the flattened tube. The longitudinal second creases can further be aligned substantially symmetrically with respect to the lateral edges of the flattened tube.
The sealing station preferably comprises a pair of belts, each belt having a run extending parallel to a part of the feed path and carrying at least one block adapted to cooperate with a corresponding block on the other belt to grasp an end portion of the bag length and to form a bottom end seal for each bag. The web of sealable material may be a heat sealable material, in which case the at least one block is heated. In addition it is further preferred for the at least one block on one belt to be arranged to cooperate with a corresponding block on the other belt to grasp the leading end of the bag length. Each belt preferably carries at least one further block which is arranged to cooperate with a corresponding block on the other belt to grasp the other end of the bag length and to deliver it positively further downstream along the feed path.
The invention further provides an apparatus for obtaining individual web sections from a web of sheet material, each web section having a predetermined process performed upon it, comprising:
(i) means for feeding a web of sheet material along a feed path to a severing station, said web carrying a succession of repeating features;
(ii) means for severing the web at the severing station at positions of said web related to said features so that individual web sections are obtained, each carrying at least one predetermined feature;
(iii) means for feeding said individual web sections to a processing station; and
(iv) means for carrying out a predetermined process at said processing station whereby a predetermined portion of each web section is maintained in registration with a processing element for a predetermined period thereby to effect said process on the web section.
Preferably the predetermined period is longer than the period between severing of that individual web section from the web and the severing of the next succeeding individual web section from the web.
A preferred form of apparatus according to the present invention comprises:
means for feeding a flattened tube along a feed path to a severing station, said flattened tube being formed from a web of sealable sheet material by sealing opposite longitudinal edge portions of the web of sheet material one to another;
means for severing the flattened tube at positions of the flattened tube related to features thereon in passage through the severing station into individual flattened bag lengths;
means for feeding the individual flattened bag lengths longitudinally further along the feed path to a sealing station; and
means for applying pressure to opposite faces of an end portion of each flattened bag length as it passes through the sealing station for a predetermined time which is longer than the period between severing that bag length from the flattened tube and severing of the next bag length from the flattened tube while continuing to feed the flattened bag length longitudinally along the feed path thereby to form a bottom seal for the bag.